The present invention relates, in general, to the accurate making of drawings of any object in conic perspective, starting either from a single view in projection revealing the three coordinates of all points, or from one plan view and another view from which the third coordinates of the various points may readily be read off.
Views in accurate perspective are desired by those who lack the possibility of imagining an object in a three-dimensional space, exactly as if they could see it in reality, although they only have at their disposal various two-dimensional views of the object.
For example, an architect has to deal with a client who wishes to have an idea of the final aspect of a building project; a modeler wishes to see in advance the part which he is supposed to model; a manufacturer wishes the views of the products available to his clients to be included in his catalogues, while his clients want to make sure, when ordering a spare part, that they use the correct reference number; an electrician or plumber wishes to have at hand a representation in perspective of the circuits according to which he has to fit pipes or electric wires; a warehouseman wishes to have at his disposal a stock card-index comprising drawings in accurate perspective of his goods, etc.
These examples demonstrate that the need for views in perspective is so general that there has always been a marked preference for this kind of representation.
The manual graphical tracing of such three dimensional drawings must be effected by experienced draftsmen, and hence such drawings are time consuming and expensive.
There exist numerous devices which can assist the draftsman in tracing drawings in perspective expeditiously, easily, and at low cost.
However, the known devices have in common the following drawbacks: complexity of the mechanical devices set into practice, e.g., bearings, pulleys, counter-cables, articulations, levers, etc., all of which soon become imperfect, bearing in mind the high degree of precision which such devices must have and maintain.
One of the co-inventors of the present invention has described a tool in this field which forms the object of French Pat. No. 1,351,371 issued Feb. 13, 1962, and of the following corresponding foreign Patents:
W. german : No. 1,461,5754 PA1 Great Britain : No. 1,037,684 PA1 Belgium : No. 636,275 PA1 U.s.a. : no. 3,226,831 PA1 Netherlands : No. 140,187 PA1 Italy : No. 711,845 PA1 Japan : No. 551,361 PA1 Switzerland : No. 400,581
Yet this patented apparatus still showed a certain number of drawbacks, even in its most advanced form, which was widely sold and which corresponds to a considerable extent to FIG. 3 of the above-cited British and U.S. patents.
In fact, the various elements of said apparatus necessarily had to be flat and superimposed one upon the other as close as possible to the plane of the drawing board over which they were moved in order to obtain a precision drawing. They also had to be made of transparent material to enable the draftsman to observe through them the dimensioned plan view on which the view in perspective was based. Yet, experience has shown that the use of such transparent elements was inadequate. Apart from being expensive, even materials of the best quality get scratched, dull and opaque after prolonged use and, above all, they often break at the various pivots and fastening means provided for them on the apparatus.
Moreover it has been necessary to pierce the drawing-board onto which the apparatus was secured.
The present invention eliminates the aforementioned drawbacks and achieves the following objects: structural simplicity which allows ease of manufacture at relatively low costs, higher ruggedness, increased precision, ease of handling, maximum visibility for the user, and a reduction to a minimum of the number of parts required to be made of transparent material, thereby considerably decreasing the risk of breaking of said parts.